Delayed Plumage Maturation Research Articles

Video evidence of mountings by female‐plumaged birds of paradise (Aves: Paradisaeidae) in the wild: Is there evidence of alternative mating tactics?

AbstractThe bewildering courtship phenotypes of male birds of paradise (Paradisaedae) represent a classic example of sexual selection through mate choice. While the majority of sexual selection studies have focused on either mate choice or intrasexual competition, males across a variety of taxa adopt alternative mating tactics as additional means of obtaining fertilization when they are otherwise unable to. For example, across various polygynous birds, subordinate males engage in sneak copulations, which may offset the fitness costs of prolonged subordinate periods. Despite exhibiting strong mating skews and male delayed plumage maturation, reports of sneak copulation in the birds of paradise are exceedingly rare. After reviewing an extensive video collection of courtship interactions, we found examples of mountings by female‐plumaged birds in three birds of paradise species: the Western parotia Parotia sefilata, Carola's parotia Parotia carolae, and the magnificent bird of paradise Cicinnurus magnificus. While homosexual mountings by females have been documented previously in Lawes' parotia P. lawesii, adult males in the magnificent bird of paradise violently attacked intruding female‐plumaged birds attempting to mount receivers, suggesting that they may be immature males engaging in alternative mating tactics. Overall, the rare video footage described here is suggestive of two fascinating, yet unexplored phenomena in polygynous birds: alternative mating tactics and female homosexual behaviour.

Age-related changes in the temporal structure of song in the common rosefinch Erythrina erythrina

AbstractBird species that have visual differences in plumage coloration between young and older males may also differ in their song parameters. We have studied the difference in song rate between yearlings vs. older males in the common rosefinch Erythrina erythrina, a species with delayed plumage maturation. Yearlings sang 2.3 more strophes per minute compared to older males, and the breaks between strophes were 1.3 s shorter in young males. The higher singing rate of yearling males is probably a form of compensation for lower age (male quality), which may be important in finding a mate or avoiding aggression from older males.

Taxonomic status of Bay-winged Hawk Parabuteo (unicinctus) unicinctus and Harris's Hawk P. (u.) harrisi, with documentation of delayed plumage maturation in Bay-winged Hawk

Taxonomic status of Bay-winged Hawk Parabuteo (unicinctus) unicinctus and Harris's Hawk P. (u.) harrisi, with documentation of delayed plumage maturation in Bay-winged Hawk

Molt strategy and delayed plumage maturation in the Lined Seedeater

Molt strategy and delayed plumage maturation in the Lined Seedeater

Why Are Snowy Owls White and Why Have They Evolved Distinct Sexual Color Dimorphism? A Review of Questions and Hypotheses

Abstract Many Arctic animals are white throughout their life, or turn white seasonally, with no distinct sexual color dimorphism. Common knowledge assumes these animals are white for camouflage in snow-covered landscapes. Presumably, this camouflage adaptation provides concealment from predators, and conversely, concealment for predation. This adaptation appears to be independent of sex. These theories seem logical; however, natural selection could also favor white coloration for other reasons. The Snowy Owl (Bubo scandiacus) is unusual because in addition to being white, it also shows sexual color dimorphism. Both sexes exhibit delayed plumage maturation. As yearlings, males and females are heavily marked with brown bars and spots on a white-based plumage. Males and females are believed to become whiter as they age. Males become almost pure white, while females retain brown bars and spots. As adults, males and females are distinctly sexually dimorphic in coloration and plumage patterning. These traits are not consistent with most other species of white Arctic animals, or most other species of owls. Snowy Owls are thought to share a common ancestor with the genus Bubo, especially Great Horned Owls (Bubo virginianus) from North America. This separation took place approximately four million years ago. If true, the evolution of white-based plumage in Snowy Owls was probably the result of natural selection favoring camouflage color in snow-covered environments, as Snowy Owls evolved and expanded into Arctic habitat. However, natural selection in concert or compromise with sexual selection, likely drove the evolution of sexual color dimorphism, and delayed plumage maturation, as a result of a snow-free tundra, and 24 hr of daylight during the breeding season. Natural selection appears to have independently favored different male and female plumage coloration and patterning. I propose that adult females evolved white plumage, interrupted with brown bars and spots, predominately for camouflage. Likewise, I propose that adult males evolved white plumage for at least two social signaling strategies: (1) to advertise their relative age, social status, and genotypic quality to females, and (2) to advertise relative age and social status to other males.

Preformative molt, plumage maturation, and age criteria for 7 species of manakins

We developed aging criteria for 7 species of manakins (Pipridae) from the Manu Biosphere Reserve, Peru, based on patterns of plumage maturation and wing-feather replacement following their preformative molt, and summarize information on their morphological characteristics. Each species underwent a partial preformative molt, which could be identified using the presence of molt limits in the greater coverts. Some male Band-tailed Manakin (Pipra fasciicauda), Round-tailed Manakin (Ceratopipra chloromeros), Cerulean-capped Manakin (Lepidothrix coeruleocapilla), and Yungas Manakin (Chiroxiphia boliviana) showed evidence of delayed plumage maturation, allowing for age classification up to the third annual cycle, whereas Blue-crowned Manakin (L. coronata caelestipileata), Fiery-capped Manakin (Machaeropterus pyrocephalus), and Green Manakin (Cryptopipo holochlora viridor) appeared to attain definitive plumage after their second molt cycle. Morphometrics showed strong overlap and were less useful for separation of age and sex classes. Our findings add to the growing list of studies that suggest many tropical passerines can be aged using primarily molt limits. Data on molt and plumage maturation are still needed for the vast majority of tropical birds in order to inform conservation-based research and studies of avian life history.

Female song is structurally different from male song in Orchard Orioles, a temperate-breeding songbird with delayed plumage maturation

Moyer, M. J., E. M. Rose, D. A. Moreland, A. Raza, S. M. Brown, A. L. Scarselletta, B. Lohr, K. J. Odom, and K. E. Omland. 2022. Female song is structurally different from male song in Orchard Orioles, a temperate-breeding songbird with delayed plumage maturation. Journal of Field Ornithology 93(1):3. https://doi.org/10.5751/JFO-00073-930103

Constraint and Function in the Predefinitive Plumages of Manakins (Aves: Pipridae).

Birds with delayed plumage maturation exhibit a drab predefinitive plumage, often despite gonad maturation, before developing the definitive plumage associated with increased reproductive success. Manakins are a diverse clade of neotropical lekking birds with extreme sexual dichromatism, radical sexual displays, and a unique diversity in the predefinitive plumages of males across species. Here, we provide the first full review of the natural history of manakin predefinitive plumages as the basis for qualitatively addressing the six major hypotheses about the production and function of predefinitive plumages. We find little evidence to support the possibilities that manakin predefinitive plumages are directly constrained by inflexible molt schedules, resource limitations to definitive coloration, or hormonal ties to reproductive behaviors. There is little evidence that could support a crypsis function, although direct experimentation is needed, and mimicry is refuted except for one unusual species in which predefinitive males sire young. Instead, evidence from a handful of well-studied species suggests that predefinitive plumages help young males explicitly signal their social status, and thereby gain entry to the social hierarchies which dictate future reproductive success. Our conclusions are especially influenced by the unique fact that males of at least 11 species throughout the family exhibit multiple predefinitive plumage stages with distinctively male patches. For each hypothesis, we highlight ways in which a better knowledge of female and young male birds offers critical opportunities for the use of manakins as a model clade.

Evolution of the preformative molt in Cardinalidae correlates with transitions from forest to open habitats

Abstract We explored adaptive factors affecting the preformative molt in the passerine family Cardinalidae, and concluded that the ancestor inhabited forest habitats and underwent a partial preformative molt that included wing coverts but not primaries. Later radiations within the family appeared to be characterized by transitions from forests toward more open habitats, and such transitions also correlated positively with increased preformative molt investment, plumage signaling, and flight. While previous studies had highlighted the role of time and energy constraints in the evolution of the preformative molt in passerines, we conclude that adaptation to the physical environment has had a greater influence than constraints on the evolution of this molt in Cardinalidae. Using molt data from 430 individuals from 41 of the 51 Cardinalidae species, we tested whether social and environmental factors (delayed plumage maturation and habitat openness), as well as that of physiological and time constraints (body mass, migration distance, and breeding latitude), have influenced the evolution of the preformative molt in this family. We predicted that these five factors could relate to the extent of the preformative molt in terms of energy investment, plumage signaling, and flight. We also examined whether or not the presence of an auxiliary preformative molt correlated to the extent of the preformative molt. We found a strong phylogenetic signal for the preformative molt in Cardinalidae due to shared ancestry, with habitat openness correlating significantly with increased molt extent. We also found a very strong relationship with the auxiliary preformative molt, indicating that both episodes form part of the early life molt strategy in this family. Evolutionary histories and the environments to which each taxonomic group has adapted can diverge across passerines, and we expect that future studies will further discover the nature and strength of the evolutionary drivers of preformative molt.

Song parameters, repertoire size and song sharing within and across age classes in the saffron finch

Birds sing mostly to attract partners or to defend territories or resources. In relation to the first function, song can vary with age if older experienced males signal their quality through their vocal output. Regarding the second function, song can also vary with age if singing behavior helps mediate social interactions through repertoire sharing with neighbors. Here, we investigate whether song parameters change with age, and in which direction, in saffron finches Sicalis flaveola pelzelni, obligate secondary cavity nesters which produce elaborate melodious songs and show delayed plumage maturation. Cross‐sectional comparisons revealed that second year (SY) males sing shorter syllables, and shorter and less versatile songs than older after second year males (ASY), as expected if the latter are more experienced singers. Longitudinal comparisons, which better depict age‐related changes, showed that as birds age one year, song length and repertoire size do not change significantly, syllable duration shortens and, as expected for experienced singers, song versatility increases. Correlations between repertoire distance and nesting distance suggest that both SY and ASY males might be adjusting their repertoires to those of ASY neighbors; the former pattern conforms to the expectations if young birds try to emulate the songs of more experienced birds, while the latter is expected if song sharing helps de‐escalating antagonistic social interactions amongst males. This research, which provides the first description of song parameters in young second year saffron finches, expands our knowledge of song variation across age classes in songbirds.

Partial or complete? The evolution of post-juvenile moult strategies in passerine birds.

Moulting strategies in birds have evolved to avoid overlap with, or prepare for, other demanding parts of the annual cycle, such as reproduction or migration. When moulting for the first time after leaving the nest, young birds replace their typically poor-quality plumage during the post-juvenile moult. The extent of this moult varies between species from partial to complete. Earlier studies, restricted to Western Palearctic birds, suggest that in most species a complete post-juvenile moult may not be possible simply because young birds are constrained by not having the same access to resources as adults, unless environmental conditions are favourable. These studies also show that complete post-juvenile moult is more common in species with poor-quality nest-grown plumage. We expanded the spatial and taxonomic scope of previous studies to 1,315 species of passerines from across the world and considered both the role of constraints, plumage quality and other selective pressures favouring a complete post-juvenile moult. Thus, we test whether complete moult is more prevalent in species where nest-grown feathers are presumably of poor quality (shorter nestling period), that live in environments that foster quick plumage degradation (open habitats, high insolation and humidity), and where males are under strong sexual selection. Our data reveal that 24% of species carry out a complete post-juvenile moult, and that this trait has a strong phylogenetic signal. Complete moult is more common in species that inhabit warmer regions and open habitats, show no delayed plumage maturation and have higher levels of sexual dichromatism (indicative of strong sexual selection). Neither the presumed quality of the nest-grown plumage nor living in regions with high insolation correlates with complete moult. In conclusion, the evolution of complete post-juvenile moult not only depends on whether birds can perform a complete moult (i.e. suitable environmental conditions) but also on the strength of selection associated with the need of a complete moult. In particular, the necessity to keep the plumage in good condition in challenging environments and the benefits associated with producing adult-like plumage colours to attract mates or deter rivals seem to play an important role.

Life history predicts flight muscle phenotype and function in birds.

Functional traits are the essential phenotypes that underlie an organism's life history and ecology. Although biologists have long recognized that intraspecific variation is consequential to an animals' ecology, studies of functional variation are often restricted to species-level comparisons, ignoring critical variation within species. In birds, interspecific comparisons have been foundational in connecting flight muscle phenotypes to species-level ecology, but intraspecific variation has remained largely unexplored. We asked how age- and sex-dependent demands on flight muscle function are reconciled in birds. The flight muscle is an essential multifunctional organ, mediating a large range of functions associated with powered flight and thermoregulation. These functions must be balanced over an individual's lifetime. We leveraged within- and between-species comparisons in a clade of small passerines (Tarsiger bush-robins) from the eastern edge of the Qinghai-Tibet Plateau. We integrated measurements of flight muscle physiology, morphology, behaviour, phenology and environmental data, analysing trait data within a context of three widespread, adaptive life-history strategies-sexual dichromatism, age and sex-structured migration, and delayed plumage maturation. This approach provides a framework of the selective forces that shape functional variation within and between species. We found more variation in flight muscle traits within species than has been previously described between species of birds under 20g. This variation was associated with the discovery of mixed muscle fibre types (i.e. both fast glycolytic and fast oxidative fibres), which differ markedly in their physiological and functional attributes. This result is surprising given that the flight muscles of small birds are generally thought to contain only fast oxidative fibres, suggesting a novel ecological context for glycolytic muscle fibres in small birds. Within each species, flight muscle phenotypes varied by age and sex, reflecting the functional demands at different life-history stages and the pressures that individuals face as a result of their multi-class identity (i.e. species, age and sex). Our findings reveal new links between avian physiology, ecology, behaviour and life history, while demonstrating the importance of demographic-dependent selection in shaping functional phenotypic variation.

The relationship between plumage coloration and aggression in female tree swallows

Intrasexual competition is an important selective force that can favor the evolution of honest signals of fighting ability. Research has focused predominantly on male birds, but many female birds also possess plumage ornaments that could mediate the outcome of competitive interactions. We examined the relationship between blue and white structural coloration and aggression in female tree swallows Tachycineta bicolor. Tree swallows are secondary cavity nesters and females show delayed plumage maturation which may be related to intense competition for nest sites. We compared plumage reflectance of second‐year (SY) and after‐second year (ASY) females, and within‐individual changes in plumage reflectance of ASY females in two successive years. We assessed aggression by placing a caged SY female 2 m from the nest box of an ASY female and quantified the ASY female's response in relation to her own plumage coloration. We found substantial differences in plumage reflectance of SY and ASY females, but found that ASY females became greener with duller white coloration in the second year. This may be due to poor weather that made reproduction particularly costly in the first year of the study and suggests coloration is influenced by condition. We found no relationship between dorsal coloration and aggressiveness. Rather, brighter white females spent more time on their nest box and within 2 m of the intruder than females with dull breasts. Our findings suggest that brighter white ASY females may perceive a SY female as less of a threat or that there may be a trade‐off associated with aggression and parental care that is related to white brightness.

Social organisation and breeding biology of the White-shouldered Fairywren (Malurus alboscapulatus)

ABSTRACTThe White-shouldered Fairywren (Malurus alboscapulatus) is a tropical passerine bird distributed across much of New Guinea. White-shouldered Fairywrens are among few species of fairywren with exclusively tropical distributions and differ from better studied congeners in Australia because subspecies vary by female, but not male, coloration and morphology. As with many bird species in New Guinea, basic demographic, social, morphological, and breeding data are limited. From 2011 to 2018 we documented the basic biology of two subspecies representing extremes of the female ornamentation spectrum. Both subspecies form groups having an even operational sex ratio and appear to breed year-round. Extra-pair paternity occurs in the subspecies with female ornamentation; comparable data are lacking for the subspecies having unornamented females, but the greater scaled cloacal protuberance volume of males suggests similar or higher extra-pair paternity rates. Females of the ornamented subspecies are generally larger than those lacking ornamentation, but exhibit reduced tail lengths, which is thought to serve as a signal of social dominance in other fairywrens. After first achieving adult-like plumage, males and ornamented females retain ornamented plumage year-round; however, only males in the subspecies with unornamented females appear to exhibit delayed plumage maturation. Our discussion highlights similarities and differences between White-shouldered Fairywren life histories and those of better studied Australian Malurus species; we focus on tropical vs. temperate environments and variable female ornamentation, and we identify priorities for future research.

Lack of conspecific visual discrimination between second-year males and females in the Saffron Finch.

Sexually dichromatic birds often show delayed plumage maturation, but second-year (SY) males may or may not be distinguishable from females. In competitive contexts, SY males receive a reduced amount of adult males’ aggression, either by mimicking females or through signaling their sex and inexperience as subordinate males. To the human eye, reproductive dull SY male Saffron Finches are indistinguishable from females, whereas after second-year (ASY) males are golden yellow. Our aim is to establish whether SY males are sexually dichromatic with females to the eye of conspecifics. We describe plumage variation in females, SY and ASY males and, in particular, analyze assortative mating by color by comparing a previously disregarded yellow feather patch shared by the three groups. We measured plumage reflectance of the forehead, breast, belly, and axillaries, and used a two-step avian visual model analysis to estimate the ability of Saffron Finches to distinguish between SY males and females. We find that those groups are indistinguishable to conspecifics by color. Furthermore, we find non-significant evidence of assortative mating directly related to the coloration of comparable feather patches between females and each type of male, though body condition of SY males is associated to that of their mates. Our results are compatible with both the female-mimicry and the status signaling hypotheses of evolution and maintenance of delayed plumage maturation. However, the singing behavior of males reveals their presence within the breeding site; the combined effect of song and dull coloration suggest that SY males are honestly revealing their sex and status to conspecifics.

Delayed plumage maturation in green‐backed flycatchers (Ficedula elisae): An evidence of female mimicry

Delayed plumage maturation (DPM) is the delayed acquisition of an adult color and pattern of plumage until after the first potential breeding period. Among the hypotheses proposed to explain DPM, the female mimicry hypothesis (FMH) has received considerable attention. FMH predicts that after-second-calendar-year (ASY) males should attack ASY males more than second-calendar-year (SY) males and females, while no difference between the two latter. Few studies have been thought as support for FMH, while in fact most of them give no conclusive evidence to the assumption of FMH that ASY males are unable to distinguish SY males from females. Thus, other support besides behavioral experiments, such as it is physiologically impossible to discriminate SY males and females from avian perspective, is important in testing FMH. We studied color differences in six plumage patches between ASY male, SY male and female by analyzing reflectance spectra in the avian visual system, and tested the prediction of FMH by conducting intrusion experiments on territorial males with three kinds of conspecifics (i.e., ASY males, SY males and females) as territory “intruders” in the green-backed flycatcher (Ficedula elisae). It is physiologically impossible for ASY males to distinguish SY males and females through the plumage color of crown, mantle, rump, and throat patches, moreover difficult to distinguish through breast and belly patches even under reasonable viewing conditions. ASY males were more aggressive toward ASY males than SY males and females with no differences between the two latter. SY males showed a slightly but not significantly higher attack intensity on ASY males than SY males and females. Our results suggest that female mimicry is more likely to be the explanation for DPM in the green-backed flycatcher. To our knowledge, this is the first study combining avian visual system and behavioral experiments in testing hypotheses of DPM.

Delayed plumage maturation explains differences in breeding performance of Saffron Finches

ABSTRACTTheory predicts that, even within the same population, birds may vary their breeding investment with age. This may be due to an improvement in individual quality of old birds in body condition, foraging and in nesting experience. Birds commonly signal age and individual quality to potential mates and competitors through plumage colour. Young male and female breeders of Saffron Finches (Sicalis flaveola) have dull plumages that change to yellow with age. We asked whether older, yellow birds are in better condition and invest more in breeding than dull, younger birds. In southern Brazil, we monitored Saffron Finches breeding in nest-boxes over three breeding seasons. We found that yellow birds were in better condition: females had more furcular fat and males were heavier. Yellow parents bred earlier, had larger clutch sizes, shorter incubation periods, re-nested more and ultimately fledged twice as many offspring as dull parents. Egg mass, nestling mass and nest survival probability were similar between plumage colours. Female colour predicted clutch sizes and incubation periods better than male colour. Our results highlight the importance of accounting for female quality and reproductive investment decisions within the context of sexual selection.

Tail pattern variation in the Black Wheatear (Oenanthe leucura)

Delayed plumage maturation occurs in birds when subadult plumage is retained until after the first breeding season. We analysed data from 114 Black Wheatears (Oenanthe leucura), which were trapped during 2014–2016 in southeastern Spain, to explore whether biometric measurements, and more specifically tail pattern, differed among age and sex classes, and whether there was a relationship between tail pattern and delayed plumage maturation. Males and adults were heavier and had longer wings and tails than females and juveniles, respectively. Adult birds had longer terminal black tail bars than juveniles, which suggests a potential dominance-signalling function for the tail pattern. Further research is needed to investigate the relationship between these traits and sexual selection and dominance in Black Wheatear.

Males in seemingly female‐like plumage do not mimic females: UV reflectance reveals temporal cryptic dimorphism in a manakin species exhibiting delayed plumage maturation

Manakins (Pipridae) are neotropical birds that usually exhibit delayed plumage maturation (DPM). Thus, while plumage of most adult male manakins is brightly conspicuous, subadult males and females are basically dull‐olive green. Although sexual dichromatism in some bird species may be evident only through UV reflectance, this phenomenon, known as hidden sexual dichromatism, has not been previously studied in manakins to compare subadult males and females. Within this framework, we carried out spectrophotometric analyses in searching for hidden sexual dichromatism in the white‐bearded manakin Manacus manacus, through comparison of UV spectra in females and subadult males in green plumage. Our results revealed UV reflectance in both sexes in green plumage. Moreover, we found UV spectral differences in homologous color patches between sexes, particularly at belly. Since the observed differences may allow intraspecific sex recognition of individuals in green plumage, our results do not support the female‐mimicry hypothesis to explain delayed plumage maturation in the white‐bearded manakin. Although our findings dismiss the female mimicry hypothesis, we cannot state whether these results support the non‐mutually exclusive cryptic and status signaling hypotheses. We propose then, that dull coloration of subadult males may serve both as a cryptic trait and to limit the energetic costs of acquiring the adult plumage before sexual maturity. Meanwhile, differential UV color traits between sexes in green plumage may allow adult males to avoid unnecessary energy expenditures in courtship displays in the presence of males near leks, and to selectively focus their the courtship displays on females. In accordance with the status signaling hypothesis, subadult males can be recognized both as males and subordinates and consequently may practice courtship displays without suffering aggressions by adult males. Our results highlight the importance to include a wider range of spectrophotometric information analyses for testing hypotheses regarding delayed plumage maturation.

Breeding Experience and not Age Modulates the Song Development of Pied Flycatchers (Ficedula hypoleuca)

In songbirds, the development of the species-specific adult song involves a learning process that varies in extension. In species that incorporate new song elements throughout life (open-ended learners), variation in male song composition could be the result of either age or breeding experience. Using data from 16 yr of fieldwork on pied flycatchers (Ficedula hypoleuca), we aimed to disclose the individual contribution of these two factors on the species song characteristics, as well as their relation with morphology and plumage color changes. Finally, we explored whether any of the song or physical features could predict the probability of males returning to the breeding site. We found that the song characteristics of the first-time breeders did not differ between age classes, except for the total number of syllables per song, which was higher in the 1-year-old than in the 2-year-old males. However, we found that song variables associated with complexity (song and sample versatilities and repertoire size), increased significantly from the first to the second breeding season. Males showed delayed plumage maturation, with 1-year-old males being browner than the 2-year-old males independently of their breeding experience. Morphology, however, was not affected by age or breeding experience. The probability that males returned to the breeding site was not associated with song or physical features. Considering that some song learning occurs during the breeding period and that some males may skip the first breeding season, selective pressures may have been established for song complexity to be an honest indicator of breeding experience rather than age.